Spark plug seat

ABSTRACT

A GASKETLESS SEAT FOR SPARK PLUGS. A RING-SHAPED RECESS IS CUT BY MACHINING OR COMMING CIRCUMJACENT AN UPWARDLY FACING SHOULDER WITHIN THE BORE OF A HOLLOW SPARK PLUG SHELL. A SPARK PLUG INSULATOR IS THEN INSERTED INTO THE SHELL UNTIL A DOWNWARDLY FACING SHOULDER ON THE INSULATOR ABUTS THE SHELL SHOULDER ADJACENT TO THE RING-SHAPED RECESS. IN COMPLETING ASSEMBLY OF THE SPARK PLUG, THE INSULATOR IS FORCED INTO THE SHELL TO DEFORM THE SHELL SHOULDER BY COLD WORKING IT AGAINST THE INSULATOR SHOULDER, THEREBY FORMING A THERMALLY CONDUCTING SEAL BETWEEN THE SHELL AND THE INSULATOR.

Oct. 5, 1971 M. AUBRETSCH 3,609,837

SPARK PLUG SEAT Filed June 16, 1969 2 Sheets-Sheet 1 INVENTCR. M JEHAEL A. BEE TECH M. A. BRETSCH SPARK PLUG SEAT Oct. 5, 1971 2 Sheets-Shoot 2 Filed June 16, 1969 a N MT T mm A .A m z my 2 M 6 A: 4 f

United States Patent 3,609,837 SPARK PLUG SEAT Michael A. Bretsch, Toledo, Ohio, assignor to Champion Spark Plug Company, Toledo, Ohio Filed June 16, 1969, Ser. No. 833,467 Int. Cl. H01t 21/00 US. Cl. 29-2512 9 Claims ABSTRACT OF THE DISCLOSURE A gasketless seat for spark plugs. A ring-shaped recess is cut by machining or coining circumjacent an upwardly facing shoulder within the bore of a hollow spark plug shell. A spark plug insulator is then inserted into the shell until a downwardly facing shoulder on the insulator abuts the shell shoulder adjacent to the ring-shaped recess. In completing assembly of the spark plug, the insulator is forced into the shell to deform the shell shoulder by cold working it against the insulator shoulder, thereby forming a thermally conducting seal between the shell and the insulator.

BACKGROUND OF THE INVENTION The present invention relates generally to spark plugs for internal combustion engines, and particularly to a gasketless seat for spark plugs.

Spark plugs generally comprise a ceramic insulatorelectrode assembly suitable mounted in a hollow, tubular metal shell. The shell usually has a reduced opening between its inner or threaded end and its opposed outer end which forms an ouwardly facing shoulder. The insulator is received by the opening in the outer end of the shell. A small metal gasket usually is placed between the upwardly facing shell shoulder and a cooperating downwardly facing shoulder on the insulator, to form a seal and an effective heat transfer path between the insulator and the shell.

In one type of spark plug that has previously been suggested in Pat. 2,020,967, the ceramic insulator is provided with a flanged portion between the downwardly facing shoulder and the outer end of the shell. The flanged portion closely engages the side wall surfaces of the large opening at the outer end of the shell and is spaced axially below the outer end of the shell to define an annular pocket for receiving a powdered sealing material. Assembly of this type of spark plug is completed by compacting a powdered sealing material, e.g., talc, into the annular pocket to force the insulator down upon the gasket and to provide a compacted powder seal. Thereafter, the outer end of the shell is crimped over the outer end of the campacted powder to hold the powder in place.

In another common type of spark plug, as is shown in Pat. 1,609,735, the insulator is provided with an upwardly facing shoulder spaced above the flanged portion. After the gasket and the insulator are placed in the shell, assembly is completed by placing an outer metal gasket on the upwardly facing insulator shoulder, crimping the outer end of the shell over the outer gasket, and collapsing the shell. The shell is collapsed by heating a thinwalled portion thereof spaced axially above the upwardly facing shell shoulder and then axially compressing the shell while it cools. When the shell is axially collapsed, the gasket between the shell and the insulator shoulders is deformed, forming a seal and a good heat transfer path.

-In a third type of spark plug, the ceramic insulator is also provided with a flanged portion which closely engages the side wall surfaces of the opening through the shell. The flanged portion is spaced below the outer end of the shell to define an annular pocket. A resilient powdered sealing material is tightly compacted into the annular pocket and the outer end of the shell is crimped over the compacted powder. The shell is then axially compressed and collapsed at a thin-walled portion located above the upwardly facing shell shoulder. As the shell collapses, the gasket between the insulator shoulder and the shell shoulder is deformed to form a seal and a good heat transfer path.

The small gasket, which is located between the insulator and the shell shoulder in each of these types of spark plugs, has been the source of a number of problems. The small physical size of the gasket has created material handling problems, and, in some instances, a defective spark plug will be manufactured because of improper placement of the gasket.

SUMMARY OF THE INVENTION to form a seat extending continuously around the insulator. In the preferred assembly method, the insulator is placed in the shell, a resilient sealing material is compacted between the insulator and the shell, and the shell is crimped over the compacted sealing material and axially collapsed by cold pressing.

In spark plug shells having small diameter openings, the ring-shaped recess preferably is cut into the shoulder with a coining die. The coining die is inserted into the outer end of the shell until it abuts the shell shoulder and a high axial force is applied between the coining die and the shell to form the recess. However, coining is less easily performed where the shell opening is relatively large because the large contact area between the die and the shell necessitates extremely high axial forces to form the ring-shaped recess. Where the spark plug shell has a relatively large diameter opening, the ring-shaped recess is preferably machined into the shell shoulder.

OBJECTS OF THE INVENTION It is a primary object of this invention to provide a method of manufacturing a gasketless spark plug.

Another object of this invention is to provide a novel gasketless seat between a spark plug shell and insulator.

Still another object of this invention is to reduce the cost of materials in a spark plug.

Other objects and advantages of the invention will become apparent from the following detailed description of a preferred form thereof, reference being had to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a coining die being inserted into a spark plug shell during manufacture;

FIG. 2 is a cross-sectional view of a spark plug shell being formed with the coining die;

FIG. 3 is a cross-sectional view of a coined spark plug shell with an insulator and a sealing material inserted therein;

FIG. 4 is a cross-sectional view showing the resilient sealing material being compacted between the insulator and the spark plug shell;

FIG. 5 is a cross-sectional view showing the upper end of a spark plug shell being crimped over the compacted sealing material; and

FIG. 6 is a cross-sectional view of a completed spark plug after the shell has been axially collapsed, as described above.

3 DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a partially manufactured spark plug shell 10 is shown positioned in a rigid holder 12. The shell 10 is preferably made of a mild steel. The lower end of the shell 10 has a threaded portion 14 with a ground electrode 16 Welded to the lower end 18 of the shell 10.

The spark plug shell 10 has a generally tubular shape with a reduced opening comprising a large diameter upper opening 20, an angled upwardly facing shoulder 22, and a small diameter lower opening 24. In a conventional spark plug, a soft metal gasket is placed on the upwardly facing shoulder 22 for forming a seat with a cooperating shoulder on the spark plug insulator. However, in accordance with the present invention to enable elimination of the gasket, a ring-shaped recess 26 (FIGS. 2-6) is so formed in the shoulder 22 that the shoulder simulates a gasket. The ring-shaped recess may be formed either by inserting a coining die 28 in the upper end 30 of the shell 10 and applying a suflicient axial force to cut the shoulder 22 to a depth ranging from 0.01 inch to 0.10 inch (preferably from 0.015 inch to 0.025 inch) or by machining. Contoured machining is usually preferred to large diameter shells for proper metal flow.

After a seat is formed in the shell 10 by forming the ring-shaped recess 26 in the shell shoulder 22, the spark plug is assembled. The first step in assembling, illustrated in FIG. 3, consists of inserting an insulator-electrode assembly 32 into the large opening 20 in the shell 10. The insulator 34 has a generally tubular shape and is made of a vitreous material. The insulator 34 has a relatively large diameter flange portion 36 adapted to fit slidably into the upper shell opening 20, but not into the lower shell opening 24. A downwardly facing shoulder 38 is located below the flange portion 36. When the insulator-electrode assembly 32 is inserted into the shell 10, the downwardly facing insulator shoulder 38 abuts the upwardl facing shell shoulder 22. In completing assembly, the insulatorelectrode assembly 32 is forced into the shell 10, deforming the shell shoulder 22 to form a seal and good contact for heat transfer. It has been found that more effective seating is obtained if the insulator shoulder 38 is glazed during the manufacture of the insulator 34. It is also preferable to have the shell shoulder 22 and the insulator shoulder 38 formed at slightly different angles, so that before assembly is completed the two shoulders have only narrow contact as indicated at a point 40 adjacent to the ring-shaped recess 26, as shown in FIGS. 3-5.

Below the downwardly facing shoulder 38, the insulator 34 has a tapered nose 42 which, when assembled, is spaced from the walls of the lower shell opening 24. A high voltage electrode 44 extends coaxially through the insulator 34 and projects from the lower end 46 of the insulator nose 42. When the spark plug is assembled, a spark gap is defined between the high voltage electrode 44 and the ground electrode 16.

Above the flange portion 36, the insulator 34 has a reduced diameter upper portion 48. An annular pocket, defined between the reduced diameter portion 48 of the insulator 34 and the wall of the upper shell opening 20, is filled with a sealing material 50, preferably a resilient inorganic particulate material such as talc or asbestos. Referring now to FIG. 4, an annular tamping tool 52 is used to compact the sealing material 50 into the annular pocket to form a resilient body.

Turning now to FIGS. and 6, a die 54 crimps the upper end 30 of the shell over the top of the compacted sealing material 50. After the end 30 is crimped, the shell is axially collapsed at a constricted portion, of reduced shell diameter by applying a high axial force to the die 54. The constricted portion 56 is spaced axially above the upwardly facing shell shoulder 22. As the shell 10 is collapsed, a high downwardly directed force is transmitted from the crimped upper shell end 30, through the 4 compacted resilient body of sealingmaterial 50, to the insulator 34. As the insulator 34 is forced down into the shell 10, the shell shoulder 22 is deformed against the insulator shoulder 38, forming an effective seat. Metal can flow both inwardly towards the insulator nose 42 and outwardly into the recess 26, giving an increased contact area between the shoulders 22 and 38. The increasedcontact area is necessary to maintain a good heat transfer path from the insulator 34 to the shell 10. The highly compressed sealing material 50 maintains a downwardly directed force on the insulator 34 and, therefore, effective seating between the shell and insulator.

Although the above described method of assembly is preferred, other Well known assembly methods may be used. In the hot pressing method of assembly, the" insulator-electrode assembly is inserted into the shell until the insulator shoulder '38 rests against the shell shoulder 22, as in the above described method. A metal gasket is then placed over the reduced diameter portion 48 of the insulator 34 and against the flange portion 36. The upper end of the shell is crimped over the metal gasket and the constricted portion of the shell is heated with an electric current and then axially collapsed, thereby deforming the shoulder 22 to form a seat and good contact for heat transfer. After the shell is collapsed, an axial force is momentarily maintained on the shell while it at least partially cools.

In a third embodiment, the insulator-electrode assembly is inserted into the shell and a high axial force'is applied to the insulator to deform the upwardly facing shell shoulder 22 into a continuous annular seat. A sealing material is then compacted between the insulator and the shell while the insulator is held in place, and the shell is crimped. Care is required in applying this assembly technique to maintain a good seat between the insulator and the shell.

It will be appreciated that other assembly methods may be used, and that various modifications and changes may be made in the shell and the insulator design without departing from the scope of the appended claims.

What I claim is:

1. A method of producing a seat in a spark plug comprising a hollow tubular shell having a reduced opening between the upper and lower ends of the shell formed by an internal, upwardly facing shoulder, and an insulator having a downwardly facing shoulder for cooperative abutment with said shell shoulder and a -flange portion above said insulator shoulder having a sliding fit with respect to the side walls of said opening above said shell shoulder, said method comprising the steps of:

(a) forming a ring-shaped recess in said upwardly facing shell shoulder;

(b) sliding said insulator into the upper end of said shell until the downwardly facing insulator shoulder abuts the upwardly facing shell shoulder adjacent said recess; and

(c) applying a suflicient axial force between said insulator and said shell to deform said upwardly facing shell shoulder into continuous engagement. with said insulator shoulder to provide an effective seatbetween said shell shoulder and said insulator shoulder.

2. The method of producing a seat in a spark plug of claim 1, wherein said ring-shaped recess is formed in said shell shoulder by inserting a coining die into the upper end of said shell until said die abuts said upwardly facing shell shoulder, and applying an axial force between said die and said shell sufiicient to form a ring-shaped recess in said shell shoulder to a depth ranging from 0.01 inch to 0.10 inch. 3. The method of producing a seat in a spark plug of claim 1, wherein said ring-shaped recess is formed in said shell shoulder by machining said recess to a depth ranging from 0.01 inch to 0.10 inch. v

4. The method of producing a seat in a spark plug of claim 1, wherein said ring-shaped recess is formed in said shell shoulder such that said shell shoulder defines an angle with the shell axis different from the angle defined by said insulator shoulder with the insulator axis.

5. A method of making a spark plug comprising a hollow tubular shell having a reduced opening between the upper and lower ends of the shell formed by an internal, upwardly facing shoulder and a constricted portion of reduced shell diameter spaced axially above said shoulder, and an insulator having a downwardly facing shoulder for operative abutment with said shell shoulder and a flange portion above said insulator shoulder having a sliding fit with respect to the side walls of said opening above said shell shoulder, said method comprising the steps of:

(a) forming a ring-shaped recess in the upwardly facing shell shoulder;

(b) sliding said insulator into the upper end of said shell until the downwardly facing insulator shoulder abuts the upwardly facing shell shoulder adjacent said recess;

(c) compacting a resilient material between said insulator, said shell and said flange to form a resilient body;

(d) crimping the upper end of said shell against the top of said resilient body; and

(e) pressing said shell by applying a downwardly directed force to said shell at a point above said constricted portion and an upwardly directed force at a point below said constricted portion to axially collapse said shell at said constricted portion, to cause the crimped upper end to hold said resilient body in a highly compressed condition and to deform said shell shoulder into continuous engagement with said insulator shoulder to provide a seal and good contact for heat transfer between said shell shoulder and said insulator shoulder.

6. The method of making a spark plug of claim 5, wherein said ring-shaped recess is formed in said shell shoulder by coining.

7. The method of making a spark plug of claim 5, wherein said ring-shaped recess is formed in said shell shoulder by machining.

8. A method of making a spark plug comprising a hollow tubular shell having a reduced opening between the upper and lower ends of the shell formed by an internal, upwardly facing shoulder and a constricted portion of reduced shell diameter spaced axially above said shoulder, and an insulator having a downwardly facing shoulder for operative abutment with said shell shoulder, and a flange portion above said insulator shoulder having a sliding fit with respect to the side walls of said opening above said shell shoulder, said method comprising the steps of:

(a) forming a ring-shaped recess in the upwardly facing shell shoulder;

(b) sliding said insulator into the end of said shell un til the downwardly facing insulator shoulder abuts the upwardly facing shell shoulder adjacent said recess;

(c) placing a gasket on said insulator above the flange portion;

(d) crimping the upper end of said shell against said gasket;

(e) heating said shell at said constricted portion; and

(f) pressing said shell by applying a downwardly directed axial force at a point above said constricted portion and an upwardly directed force at a point below said constricted portion to axially collapse said shell at said constricted portion and to deform said shell shoulder into continuous engagement with said insulator shoulder to provide a seat between said shell shoulder and said insulator shoulder.

9. A method of making a spark plug comprising a hollow tubular shell having a reduced opening between the inner and outer ends of the shell which forms an internal, upwardly facing shoulder, and an insulator having a downwardly facing shoulder for operative abutment with said shell shoulder and a flange portion above said insulator shoulder having a sliding fit with respect to the side walls of said opening above said shell shoulder, said 0 method comprising the steps of:

(a) forming a ring-shaped recess in the upwardly facing shell shoulder;

(b) sliding said insulator into the outer end of said shell until the downwardly facing insulator shoulder abuts the upwardly facing shell shoulder adjacent said recess;

(c) applying a sufficient force between said insulator and said shell to deform said shell shoulder, thereby forming a seat between said shell shoulder and said insulator shoulder;

(d) compacting a resilient material between said insulator and shell on top of said flange to form a resilient body; and

(e) crimping the outer end of said shell against the top of said resilient body.

References Cited UNITED STATES PATENTS 1,269,782 6/1918 Braselton et al. 313144 2,020,967 11/1935 Rohde 313-144X 2,875,365 2/ 1959 Pierce 313-145 FOREIGN PATENTS 1,139,088 2/1957 France 313144 RAYMOND F. HOSSF'E-LD, Primary Examiner U.S. Cl. X.R. 313144 

